Dont have answer for you but I have one doing the same thing. My Jersey giant has always roosted at night but is in the middle of a pretty strong moult and now she is sleeping in the end nest box. Maybe they feel warmer in a nest box with less feathers than a perch?

I noticed the same thing as my girls started molting, and it does not seem to make a difference if it is a bird who loses them all in a short time, or slowly over months. I suspect they are trying to stay away from the roosters and the curious non-molting younger birds who peck at the bald spots.